1. Field of the Invention
The present invention relates to an apparatus to position and secure a sub-chassis within a chassis.
2. Background of the Related Art
An electronic device within a computer system may be connected to other electronic components through connectors that enable the communication of data signals therebetween. For example, a first electronic device, having a connector thereon, may send signals through the connector and to a second electronic device also having a connector that is engaged by the connector on the first electronic component. Connectors come in a variety of configurations including, but not limited to, pin and socket connectors, pin and sleeve connectors, parallel port, USB and serial connectors, to name a few. The connectors of the first electronic component and the second electronic component may be directly engaged or indirectly engaged through an intermediate structure, such as a midplane installed in a chassis.
A midplane is generally an electronic interface board installed within a chassis to support one or more connectors on a front side and one or more connectors on a back side. An electronic device having a connector may be coupled to a connector on the front side of the midplane in order to enable communication with one or more other electronic device having a connector coupled to a different connector on either the front or back side of the midplane.
For example, the connector of a first electronic device having a circuit board may include a row of elongated conductive pads aligned along an edge of the circuit board to be received into a socket connector on the front side of a midplane to engage the row of pads with a corresponding row of signal pins within the socket. A second electronic component, such as a network switch having a pin and sleeve connector, can be connected to a connector on the back side of the midplane to enable electronic communication between the network switch and the first electronic device through circuitry within the midplane. A midplane provides for convenient installation, maintenance and substitution of electronic devices in a chassis without having to remove or manipulate other electronic devices and without having to handle and manage a large number of cables.
As the frequency of electronic signals continues to increase, and as the voltages associated with these signals decreases, electronic noise becomes more of a concern. High-speed and low-voltage signals are more susceptible to electronic noise disruption than are low-speed and high-voltage signals. One source of electronic noise relates to conductive stubs. A stub is a portion of a conductor that extends beyond the true point of contact between two conductive members. In a connector, a stub can result from the need to accommodate electronic component connector tolerances. For example, as an edge of the circuit board is received into a corresponding socket to engage a row of pads along the edge of the circuit board with a corresponding row of signal pins within the socket, each pad initially engages the corresponding signal pin and then slides or “swipes” along the signal pin until the card is secured in an operable position. The resulting “true” point of contact between a pad and a corresponding signal pin may leave a stub comprising the portion of the conductive pad that extends past the point of true contact with the signal pin. The stub is not in a direct conductive pathway between the true point of contact and the electronic device, and is not a useful part of the circuit. However, a stub of this type can be the source of unwanted electronic signal reflections in a high-speed, low-voltage electronic signal.
Connectors for electronic devices are generally manufactured to function notwithstanding minor variations in the physical dimensions of the connectors or the electronic components that are electronically coupled through the connectors. For example, a socket on a midplane and a card edge of a circuit board to be received into the socket are each manufactured within certain tolerances to ensure that the card edge of the circuit board will fit within the socket and to ensure that when the card edge is received within the socket, the pads along the card edge conductively engage the corresponding signal pins within the socket. To ensure conductive engagement, the pads along the card edge are generally elongate along the direction of the card edge insertion so that any variance in the dimensions of the circuit board, socket, or relevant chassis does not prevent conductive contact between the pads and the signal pins. As a result, a substantial portion of each pad along the card edge may engage and then move past the true point of contact with the corresponding signal pin to create a stub. The length of each of the elongate pads in the direction of insertion of the card edge may be referred to as the “swipe” of the pad because the action of the pad “swipes” along the signal pin as the card edge of the circuit board is inserted into the socket.